The present invention relates to miniature linear guide devices adapted for use in comparatively small devices such as computer-related devices, office automation equipment, measuring instruments, drafting equipment, and semiconductor manufacturing systems. More particularly, the present invention is directed to an improved structure for mounting a guide rail thereof and an improved profile of a slider thereof.
A conventional miniature linear guide device is for instance as shown in FIGS. 8 to 10. The linear guide device is assembled with a guide rail 1 substantially U-shaped in section which is extended in a longitudinal direction (or axial direction) of the device by press molding a thin steel plate, and a slider 2 slidably mounted on the guide rail 1. The slider 2 provides: a slider body 3 substantially inverse-U-shaped in section which is formed of a thin steel plate by pressing; a circulator 4 which is formed of plastic by molding and has ball circulating paths therein; and a cap 5 which is formed of plastic. The circulator 4 and the cap 5 are fitted in a concave portion of the slider body 3 so that the cap 5 is interposed between the slider body 3 and the circulator 4.
Load ball rolling grooves 1B and 3B are formed in the inner surfaces of both side walls of the guide rail 1 and in the outer surfaces of both side walls of the slider body 3, respectively, in such a manner that those grooves 1B and 3B are extended in an axial direction of the guide device and confronted with each other. A plurality of balls 6 are fitted in the load ball rolling grooves 1B and 3B and in the ball circulating paths in the circulator 4. The balls 6 are infinitely circulated while being rolled so that the slider 2 is linearly moved along the guide rail 1.
As shown in FIG. 9, the guide rail 1 is fixed by inserting screws B1 into mounting holes 1d of a bottom la of a rail, and tightening the screws into screw holes of a base. On the other hand, the slider 2 is mounted on other member such as a machine table by screwing screws into mounting screw holes 3e formed in the top of the slider body.
Since the miniature linear guide device is generally used in a small space, it is demanded that the height thereof be as small as possible. Therefore, as shown in FIG. 9, a distance .alpha. between the bottom of the guide rail 1 and that of the slider 2 is set to a small value. However, since the guide rail 1 is mounted on the base by causing the head of each screw B.sub.1 inserted into the mounting hole 1d of the bottom 1a of the rail to be accommodated in this small gap .alpha. in the conventional linear guide device, there has been a limitation on the size of the screw B.sub.1 that can be used without interference with the slider 2. It is for this reason that the force for fastening the guider rail with the base cannot be increased by increasing the size of the screw B.sub.1 under operating conditions in which vibration and impact are applied. In addition, the guide rail tends to deformation by the screw tightening force applied at the time of mounting the guide rail.
To overcome these conventional problems, it is conceivable to, e.g., increase the thickness of the wall of the guide rail 1 so that the heads of the mounting screws can be embedded completely into deep spot facing holes. However, such a manner entails an increase in height, cost of manufacture, and the like. On the other hand, it is also conceivable to weld mounting plates on the outer surfaces of the side walls of the guide rail. However, such a manner involves a welding process in forming the mounting sections, which not only increases the cost of manufacture, but also causes deterioration in accuracy and the like due to the guide rail being subjected to thermal distortion.
Further, to reduce the height of the linear guide device, not only the mounting holes 1d in the bottom 1a of the guide rail 1 are formed into spot facing holes, but also a shallow recess M in the middle in the axial direction of the bottom of the slider 2 is arranged as shown in FIG. 9, so that the heads of the rail mounting screws B.sub.1 can be accommodated in the gap .alpha. between the bottom of the guide rail 1 and that of the slider 2 to prevent interference of the screws B.sub.1 with the slider 2 while the slider 2 is travelling over the screws B.sub.l.
However, in the case where a particularly small height is required, it is sometimes taken such that the slider 2 is stopped before the slider 2 reaches the screws B.sub.1 to prevent interference and the thicknesses of the guide rail 1 and the slider 2 are reduced by a value substantially equal to the gap .alpha.. In this case, the maximum stroke of movement of the slider 2 is determined by the positions at which the end of the slider 2 interferes with the rail mounting screws B.sub.1. Since the end faces of the conventional slider 2 are flat, the effective stroke L.sub.s of the slider 2 is equal to a length (L-l.sub.s) obtained by subtracting the total length l.sub.s of the slider 2 from the distance between the heads of the rail mounting screws B.sub.1 mounted on both end portions of the guide rail 1.
By the way, it is often required that the effective stroke be as long as possible while making the height as small as possible. This requirement can be simply met only by increasing the length of the guide rail 1. However, since most miniature linear guide devices are used in extremely small spaces, it is, in reality, difficult to increase the length of the guide rail.
On the other hand, it is also conceivable to decrease the length of the slider 2 instead of increasing the length of the guide rail 1. In this case, the length of each load ball rolling groove 3B is decreased as much as the length of the slider 2 is decreased. As a result, the number of load balls 6 (the effective number of balls) is decreased, which in turn reduces load capacity of the linear guide device.
Moreover, inaccuracy in molding the curved grooves of the conventional circulator due to shrinkage cavity at the time of molding has imposed a problem of the operability of the balls.